Differnt 4l80e

[Yukon6.2]

Hi
Looking for some direction as to things to check.New to me truck,1996 2500 2wheel drive 6.5 285000 kms.
Has some issues that i would like to try to find.
Trans oil is cleen and dosn't smell burnt.
Took it for a drive after it was warm, it will move frwards and back fine untill you go to fast or the engin over revs,that is more revs than the speed your going,then it will not move till you shut it off and restart.So long as you drive it slow you get one shift forwards and will drive ok till you over rev then it's shuit off and restart.
It shows the check engin light but havn't pulled any codes,not sure when i'll be able to pull them.
Did notice that the throttle seems to fall off with out changing possition of your foot.
Don't plan on using this truck for much,especially if the tranny is hooped,it will become a donner.
But i always hate to condem a truck that might work a few more miles,it's complete and i did a neanderthall body job on the box side that had been pushed in so it dosn't look as bad as it did two days ago:D
Thanks Thomas

[More Power]

As a first step in troubleshooting, most recommend pulling the pan, changing the filter, then refill with new ATF. A plugged filter can cause the symptoms you're seeing. If the trans is original, it could be simply worn out and due for a rebuild, assuming it has the number of Kms you're reporting. I'd try a new filter first.... The amount of sediment coating the inside bottom of the pan will give you an indication of how long it's been since the last service and how much of the clutch material has worn away and settled onto the pan. Save the original pan seal (if it's original). The factory pan seal is reusable (it's aluminum with an o-ring) and is much better than the composition gaskets you'll find at an auto parts store.

Jim